Racing Tides for Sea Stars

Setting up science is a tricky task when your study site appears for a brief window once a month.

Conducting science in the intertidal zone is a race before your study site disappears. The tide clock counts down the time you have left to finish. Even when you have an exact plan, finishing a day’s work can be tricky—but it’s an extra challenge when setting up a new project.

It’s a relief when I finally hear a faint voice amid the deafening sound of wind baffling my hood and rain playing a beat on my Gore-Tex. “That’s thirty meters!” We’ve finally found a suitable stretch of bedrock.

Our team of four is perched on a rocky headland on an eastern shore of Quadra Island, British Columbia, to set up the first of three permanent plots to monitor for sea star wasting—that fast-moving marine epidemic that swept the west coast of North America in 2013 and 2014, turning sea stars into piles of goo. Sites are marked with bolts that are drilled and cemented into the rock: 30-meter-long swaths of shoreline, from the waterline at the lowest of low tides to the high-tide mark. Inside each plot, every sea star is counted, measured, and given a classification for how wasted it is, if at all. 

Sea star wasting disease (SSWD) was most evident when it first came on the scene in 2013. Suddenly, swaths of iconic echinoderms like ochre and sunflower stars developed lesions, lost limbs, and melted. Despite the recovery of some species in some places, the disease never really went away. The sunflower star, in particular, has now all but disappeared from much of the southern part of its range, and in 2020 was listed as critically endangered by the International Union for Conservation of Nature. This latest project on Quadra Island is part of efforts by coastal scientists from Alaska to California to track the disease and any possible places where sunflower stars are recovering.

First photo: As one of the species most impacted by sea star wasting, ochre stars (Pisaster ochraceus) are a main focus during surveys. Photo by Kelly Fretwell. Second photo: Research technicians set out transect tapes to figure out where to set up a permanent sea star survey site in Hyacinth Bay on Quadra Island. Photo by Carolyn Prentice

The tidal clock also sets limits on the potential days available to pick sites. There are only four days during which the tide dips sufficiently below one meter where sea stars most like to hang out. And these four days, the first good tides this spring, are just enough time to find one site each day, plus one spare day for bad weather.

Choosing a site seems like it should be the easy part. After all, sea stars, especially ochre and leather stars, are commonly found all over the island—even now, after sea star wasting has taken its toll. We know from previous recon that plenty of sea stars hang out in these spots, and we had studied the site maps and talked over possible spots to set up. But trying to set out on the ground what had been visualized from the bird’s-eye view of satellite imagery is a tricky task—especially when your potential site will disappear below the surface before too long.

“It’s definitely hard to get the lay of the land,” says research technician Carolyn Prentice, who months earlier had braved mid-winter nighttime low tides for the initial recon.

We need to choose areas that hit the sweet spot of good for our many-armed subjects—rocky, good exposure to waves, enough cracks and crevices to tuck themselves into—and good for humans—namely safe. Pick the wrong kind of habitat, and you risk misrepresenting sea star population trends. After all, it doesn’t say much that there are no sea stars in an alpine meadow. 

Research technicians Carolyn Prentice (left) and Gillian Sadlier-Brown (right) drill and cement bolts into the low intertidal as the rising tide creeps closer. Photos by Kelly Fretwell

So like intertidal Goldilocks, we spend much of our precious low-tide time trying to find the best stretch of bedrock. One spot has too much cobble: while sea stars can be found on and under cobble, this would require a whole different survey protocol, and wouldn’t allow for valuable comparisons to other sites. Another stretch is too steep: not even the most practiced and sure-footed of technicians could balance, mountain goat-like, on the seaweed-covered rock and not slip. Yet another spot is a bit too exposed: swell would be funneled straight to the survey site and cut off access to low-tide rocks, where stars are most likely to be found.

“It seems simple to set up a 30-meter transect tape, but definitely a lot more thought was required than I expected,” says Prentice.

After many adjustments of transect tapes, all the while keeping one eye on the water level, we find the “just right” sweet spots at each location. We drill and cement bolts into the shoreline to mark the plot boundaries, then watch as the ocean reclaims the rock where we just finished working, not to be seen again until next month when the ocean dips low enough once more.